Electronic devices, which include a chip component joined to a substrate, are often vulnerable to crack formation. In particular, cracks tend to appear along the bond lines around attachment structures such as bumps, including either between the bump and the component or between the bump and the substrate. Cracks may occur in manufacturing or use when the materials of the substrate and/or electronic device are subjected to thermal cycling and expand and contract at different rates. Such cracks are a major source of device failure in chip components. For instance, cracks in a substrate can damage dielectric layers inside the substrate. In addition, mechanical stress due to coefficient of thermal expansion (CTE) mismatch can cause delamination in multiple device stack layers on a die. Underfill techniques and materials are extensively used in semiconductor manufacturing in an effort to stabilize chip components and help prevent device failure.
One common underfill technique is “capillary underfill”. Capillary underfill typically involves flowing an adhesive material between the component and the substrate, so that it contacts both the component and the substrate as it is drawn into and through an intervening gap by a wicking action. When functioning properly, the underfill will migrate completely beneath the component, displacing all air and reaching to all the edges of the chip component. The underfill may then be cured to form a substantially rigid material surrounding and strengthening each attachment joint. This can allow the materials to better withstand the stresses applied to attachment structure bond lines during thermal variation, and protect against delamination in multiple device stack layers on a die. At each edge of the component, a generally concave fillet of underfill material may form, extending from the component to the substrate surface only a short distance beyond the peripheral boundary of the component.
After it is dispensed, the flowable adhesive may flow not only into and through the gap between the component and the substrate, but also away from the dispense point and the component, across the surface of the substrate. Once cured, this “counter-directional” flow forms an “extended fillet” of underfill material. This generally unimpeded flow away from the component necessitates, in many instances, the use of more underfill than is necessary to simply fill the component-substrate gap, and the underfill material comprising the extended fillet is essentially wasted. Further, the area covered by the extended fillet is generally designated a “keep out zone” (KOZ) into which no other components are placed to avoid potentially damaging them. Therefore, on the side of a chip component where an extended fillet of underfill material forms, the substrate surface area beneath the extended fillet is effectively made unavailable for component placement and essentially wasted.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope or to specific invention embodiments is thereby intended.